Go Mi Nyu is a sister-in-training. When her identical twin brother Go Mi Nam successfully auditions into the musical band A.N.JELL but is forced to leave for the United States to correct a botched plastic surgery effort, she is approached by his manager to pose as Mi Nam for the duration of his recovery. Against her wishes, Mi Nyu accepts in order to fulfill her brother's dream of finding their mother. Now, posing as Mi Nam, Mi Nyu enters the group A.N.JELL and meets its members; Hwang Tae Kyung, Kang Shin Woo and Jeremy.

Initially disliked by Tae Kyung, the group's leader and composer, Mi Nyu slowly falls in love with him, only to find herself entangled in a love triangle between him and Shin Woo. Jeremy also harbors a one-sided love for her despite not knowing she's a girl. Additionally, Mi Nyu finds herself rivaled against Yoo He Yi, an actress who also has feelings for Tae Kyung.